1. Field of the Invention
The present invention relates to a mobile communication system and, in particular, to an adaptive modulation coding apparatus for providing multimedia communication services in a mobile communication network.
2. Related Art
In a mobile communication system, mass capacity of transmission data and acceleration of data transmission speed are required to deal with the need for various multimedia services. Accordingly, methods are needed for using a limited frequency efficiently. One of the methods is AMC (adaptive modulation and coding) scheme. The AMC scheme is for varying encoding and modulating methods according to variation of forward channel characteristics.
FIG. 1 is a block diagram illustrating an AMC apparatus for a general mobile communication system. The AMC apparatus comprises an AMC receiver 10 for estimating forward channel characteristics by using a reception signal received through a reception antenna. AMC receiver 10 selects a level of a MCS (modulation coding scheme) according to the estimated forward channel characteristics and provides a feedback of the estimated forward channel characteristics. AMC receiver 10 also demodulates and decodes the reception signal. The AMC apparatus also includes an AMC transmitter 20 for selecting a level of a MCS according to the feedback forward channel characteristics, and coding and modulating transmission data according to the selected MCS level.
The AMC receiver 10 includes a channel estimator 12 for estimating forward channel characteristics by way of a reception signal received through the reception antenna 11. The AMC receiver 10 also includes a demodulator 13 for detecting a demodulation method according to the forward channel characteristics estimated in the channel estimator 12. The AMC receiver 10 demodulates the reception signal according to the demodulation method. A channel deinterleaver 14 for channel-deinterleaving the reception data demodulated in the demodulator 13; and a decoder 15 for decoding the reception data outputted from the channel deinterleaver 14, may also be included in the AMC receiver 10.
The AMC transmitter 20 includes a MCS level selector 21 for selecting a MCS level, according to the forward channel characteristics transmitted from the AMC receiver 10. The AMC transmitter 20 also includes an encoder 22 for encoding transmission data according to a pertinent coding rate of the feedback MCS level from the AMC receiver 10, a channel interleaver 23 for channel-interleaving transmission data encoded in the encoder 22 according to the MCS level, and a modulator 24 for modulating the transmission data outputted from the channel interleaver 23 according to a pertinent modulation method of the MCS level and transmitting it to a transmission antenna 25.
The AMC receiver 10 is included in a mobile communication terminal, and the AMC transmitter 20 is included in a base station. The base station can perform the MCS level selecting by feedback-receiving SNR (signal noise ratio) of a forward channel from the mobile terminal. The mobile terminal can perform the MCS level selecting according to the estimated SNR of the forward channel to provide feedback to the base station.
First, a method for classifying a MCS level according to channel characteristics will be described. FIG. 2 shows a method for classifying each MCS level according to a FER (frame error rate) about a SNR level and throughput. For example, when a channel SNR is not less than 3.25 dB and not greater than 7.25 dB, a 2/3 encoding ratio-QPSK (quadrature phase shift keying) modulation method has a throughput greater than that of an 1/3 encoding ratio-QPSK modulation method.
In addition, when a channel SNR is not less than 7.25 dB and not greater than 9.25 dB, a 2/3 encoding ratio-8PSK (phase shift keying) modulation method has a throughput greater than that of the 2/3 encoding ratio-QPSK modulation method. When a channel SNR is not less than 9.25 dB, a 2/3 encoding ratio-16QAM (quadrature amplitude modulation) method has a throughput greater than that of the 1/3 encoding ratio-QPSK modulation method.
Accordingly, when a channel SNR is not greater than 3.25 dB, the 1/3 encoding ratio-QPSK modulation method is selected. When a channel SNR is not less than 3.25 dB and not greater than 7.25 dB, the 2/3 encoding ratio-QPSK modulation method is selected. When a channel SNR is not less than 7.25 dB and not greater than 9.25 dB, the 2/3 encoding ratio-8PSK modulation method is selected. When a channel SNR is not less than 9.25 dB, the 2/3 encoding ratio-16QAM modulation method is selected.
FIG. 3 is a table showing MCS levels with reference to FIG. 2. As depicted in FIG. 3, a MCS level 1 shows the 1/3 encoding ratio-QPSK modulation method. A MCS level 2 shows the 2/3 encoding ratio-QPSK modulation method. A MCS level 3 shows the 2/3 encoding ratio-8PSK modulation method, and a MCS level 4 shows the 2/3 encoding ratio-16QAM modulation method.
Hereinafter, the operation of the adaptive modulation coding (AMC) apparatus of the general mobile communication system will be described. The channel estimator 12 of the AMC receiver 10 estimates the forward channel characteristics by using the reception signal from the reception antenna 11. The estimated forward channel characteristics are provided by the mobile terminal to the AMC transmitter 20 of the base station.
The demodulator 13 of the AMC receiver 10 detects a demodulation method according to the estimated forward channel characteristics and demodulates the reception signal according to the detected demodulation method. The demodulated reception signal is decoded through the channel deinterleaver 14 and the decoder 15.
When the AMC transmitter 20 receives the MCS level transmitted from the AMC receiver 10, the MCS level selector 21 of the AMC transmitter 20 selects an optimum MCS level according to the forward channel characteristics. Encoding, channel interleaving and modulation of the forward channel are thus performed according to the selected MCS level.
The encoder 22 of the AMC transmitter 20 encodes transmission data according to a pertinent encoding ratio of the MCS level. The channel interleaver 23 performs channel-interleaving of the encoded transmission data according to the MCS level. The modulator 24 modulates the transmission data according to a pertinent modulation method of the MCS level and transmits the modulated transmission signal (i.e., transmission symbol) via the transmission antenna 25.
As described above, in the adaptive modulation coding (AMC) apparatus of a general multimedia communication system, transmission performance can be improved by varying modulation and coding schemes according to channel characteristics. However, it is difficult to correspond to acceleration of data transmission speed required for providing various and rapid multimedia services with the transmission performance improvement by the AMC scheme.